For login to Stack Overflow I use Yahoo's OpenID service. Today, I tried to register on Stack Overflow with my Facebook account. When I allowed Facebook to give my information to Stack Overflow, I was logged in to my Yahoo account.

In this case, Stack Overflow used my email to register me and my email was in the Stack Overflow users database so I logged in to main account (Yahoo) and now I have two OpenID acounts.

When a user has not confirmed his email on Facebook, is this process also correct? If yes, some users can login to another account with faked Facebook account to the Stack Overflow.